VW Polo problem

[Velocette]

We have a 2008 1.4 Polo as a runabout vehicle,,62.000 miles of lady ownership,,which has developed a very baffling fault. First thing in the morning it starts perfectly,as it does at any time when the engine is warm/hot. However,,if its a hot day,,like today,,left for 5 or 6 hours in the sun,its very reluctant indeed to start. It makes no sense to me but perhaps someone has come across it and knows the answer.

[wisdom]

Fuel vaporising somewhere in the engine bay at a guess or fuel running back from the pump.

[Me matt]

Go to Euro carparts and get one of their £30 fault code readers and plug it in, they are great for everything VAG 👍 if your local to Chelmsford I have one you can use.

[Velocette]

Go to Euro carparts and get one of their £30 fault code readers and plug it in, they are great for everything VAG if your local to Chelmsford I have one you can use.

 

We've just had it in the local VW garage and they couldn't get any fault code up on the diagnostic machine. A very kind offer though .

[Velocette]

Fuel vaporising somewhere in the engine bay at a guess or fuel running back from the pump.

 

Any thoughts as to where this vaporisation might be happening because that's exactly what it seems like. I thought that the engine bay would be pretty warm when the motor is running and going slowly in heavy traffic but no problems arise then. As for the fuel pump,,is there any way of checking to see that its working properly?

[Rupert]

MAF.

[johnnytheboy]

Have you tried the old process of elimination, check for a spark from the plug, if your getting one then it's ok, feed fuel direct to the engine to see if it starts to fire on the fuel your feeding it etc

[Me matt]

MAF.

VAGCOM at the dealers would have picked that up.

[Me matt]

 

Any thoughts as to where this vaporisation might be happening because that's exactly what it seems like. I thought that the engine bay would be pretty warm when the motor is running and going slowly in heavy traffic but no problems arise then. As for the fuel pump,,is there any way of checking to see that its working properly?

Fuel pump access panel should be under rear seat- it'll be an in tank pump. Although I would have thought the VAGCOM diagnostics at the dealers would have picked up low fuel pressure 🤔 you could try replacing the fuel filter - easiest option and quite a common fault.

[Velocette]

Fuel filter sounds sensible,,but apart from a reluctance to start with a cold engine on a hot day,,it runs perfectly. No lumpiness,,doesn't cut out,,fuel consumption is fine. I know it seems crazy,,but if its not a hot day,or its parked in the shade on a hot day,,it starts as it should.

[Rupert]

Some kind of temp sensor for the cold start fueling?

[Velocette]

That's what it seems like,,,though I've just replaced the engine coolant temp. sensor as these are prone to weakness. Its as if some sensor is mistakenly telling the cold engine that its warm,,,but only when that sensor is sun warmed. When its stone cold in the morning and the sun isn't up the engine is being fuelled correctly and it starts straight away. When the engine is hot,wherever the car is,it starts perfectly so the fuelling ought to be fine. Its just when the car has stood for most of the day in an exposed to the warm sun position that it plays up and takes age age to stir into life. Odd isn't it !!!!!

Edited April 23, 2017 by Velocette

[rovercoupe]

I have a 2001 1.4 engine sat here if you need any sensors off it to try, a spark test would be a good place to rule out a fault and it will not throw a fault code if intermittent. They are a pain in the **** to fault find these cars, i hate my other halfs!

[Velocette]

That's a very kind offer,,if I can get to the point of identifying which one it may be I'll be in touch. Thanks .

[gustaff]

engine coolant temp sensor just plugs into thermostat housing with a plastic clip 5 minute job scanner with live time data will correctly diagnose no fault codes as sensor not totaly failed just reading wrong

[Velocette]

Thanks for the suggestion but I have fitted a new sensor and the problem is still there,,,on a hot day with a cold engine !!!!

[Del T]

We had something like this on an old car. Ended up being the seal on the petrol filler cap.??

[Me matt]

Have you done fuel filter? A little test you can try is - when it's playing up and running rough/won't start - undo the fuel cap, see if you hear a big hiss of suction. Could be blocked breather, the earlier polos had really poorly designed tanks, I replaced loads at my workshop due to the filler necks rotting out.

[Velocette]

Now that sounds promising,,,I had the same sort of problem with my Jimny which was a blocked breather on the fuel tank. FINGERS CROSSED !!!!

[Me matt]

I've resolved the same problems on loads of VW,S in the past, air cooled one's being the most sensitive to it, can destroy a flat four within a few weeks if not diagnosed in time. Don't overlook the fuel filter though, can do a flow test to check the pump while it's off too 👍

[Me matt]

Now that sounds promising,,,I had the same sort of problem with my Jimny which was a blocked breather on the fuel tank. FINGERS CROSSED !!!!

Any updates on the poorly polo?

[Velocette]

We've been loosening the filler cap before each start,,but as its been so cold here these last few days I didn't expect the problem to arise. Its due to get warmer this weekend so hopefully we can do a realistic test with the vented filler cap on a warm day. Failing that I plan to sacrifice a black cockerel at midnight and dance naked around the car. Please don't even try to imagine that !!!

[Me matt]

Failing that I plan to sacrifice a black cockerel at midnight and dance naked around the car. Please don't even try to imagine that !!!

Ah- the factory reset option never fails 🤣